The effectors responsible for intestinal adaptation include luminal contents, endogenous secretions, hormones, neurovascular factors as well as the metabolic status of the organism. Research from many laboratories, including our own, has indicated that luminal nutrients and metabolic balance are the principal stimuli for change. This project will study the specificity of luminal contents necessary to maintain intestinal absorption and mass. At present, we do not know whether active vs passive absorption or the metabolism of absorbed nutrients are necessary to bring about adaptation. The objectives of this study are: 1) To examine the effects of active and passively absorbed substrates, as well as metobolizable and non-metabolizable substrates on intestinal function, both in vitro and in vivo. 2) To examine the effects of metabolic balance and luminal nutrition by comparing fasted rats to rats maintained by parenteral or enteral nutrition. In order to better understand these phenomena, in vitro studies designed to investigate the kinetics of the initial velocity of active transport will be carried out. In vivo perfusion experiments designed to determine the luminal and metabolic factors regulating net intestinal transport of sugars and amino acids will be performed also. The animal model used for these studies will be the parenterally nourished rat. In addition, intestinal catheterization of the jejunum or ileum will be performed so as to infuse a single solution into the intestinal tract in order to determine its effect on absorptive function. The long term objectives of these studies are to allow better nutritional support of patients requiring enteral and parenteral nutrition, such as inflammatory bowel disease and the short bowel syndrome. These studies have the fundamental objective of achieving a better understanding of the regulation of intestinal transport.